AIM: Obesity does not always signify increased cardiovascular risk

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Some obese individuals do not appear to have an increased risk for heart disease, while some normal-weight individuals experience a cluster of heart risks, according to two reports in the Aug. 11/25 issue of Archives of Internal Medicine.

Research has indicated that in addition to overall obesity, the way body fat is distributed may influence risk for heart disease and diabetes. Individuals with fat within the abdominal cavity appear to be at higher risk for insulin resistance and for having an unhealthy cardiovascular risk profile, according to the researchers.

In one study, Norbert Stefan, MD, and colleagues at the University of Tübingen in Germany, studied 314 individuals age 18 to 69 (average 45, measuring participants’ total body fat, visceral fat and subcutaneous fat using MR tomography. Insulin resistance was measured using an oral glucose tolerance test. The individuals were then divided into normal weight, overweight, obese but still sensitive to insulin and obese with insulin resistance groups.

Those in the overweight and obese groups had more total body and visceral fat than those at a normal weight, and there was no difference between obese groups, the authors wrote.

However, Stefan and colleagues found that obese individuals with insulin resistance had more fat within their skeletal muscles and their livers than obese individuals without insulin resistance. In addition, those who were insulin-resistant had thicker walls in their carotid arteries, an early sign of atherosclerosis.

In a second study, Rachel P. Wildman, PhD, of the Albert Einstein College of Medicine in Bronx, N.Y., and colleagues assessed body weight and cardio-metabolic abnormalities (including, high blood pressure, elevated triglycerides and low high-density lipoprotein) in 5,440 individuals participating in the National Health and Nutritional Examination surveys between 1999 and 2004.

The investigators assessed the participants as metabolically healthy if they had none or one abnormality and metabolically abnormal if they had two or more abnormalities.

“Among U.S. adults 20 years and older, 23.5 percent (approximately 16.3 million adults) of normal-weight adults were metabolically abnormal, whereas 51.3 percent (approximately 35.9 million adults) of overweight adults and 31.7 percent (approximately 19.5 million adults) of obese adults were metabolically healthy,” the authors wrote.

Wildman and colleagues said that normal-weight individuals with metabolic abnormalities tended to be older, less physically active and have larger waists than healthy normal-weight individuals. Obese individuals with no metabolic abnormalities were more likely to be younger, black, more physically active and to have smaller waists than those with metabolic risk factors.

“These data show that a considerable proportion of overweight and obese U.S. adults are metabolically healthy, whereas a considerable proportion of normal-weight adults express a clustering of cardiometabolic abnormalities,” Wildman and colleagues wrote. “Further studies into the behavioral, hormonal or biochemical and genetic mechanisms underlying these differential metabolic responses to body size are needed and will likely further the identification of possible obesity intervention targets and improve cardiovascular disease screening tools.”

Both studies attempt to improve the understanding of obesity by calculating body mass index and measuring waist circumference, to more accurately predict which patients will develop cardiovascular disease, wrote Lewis Landsberg, MD, of the Northwestern University Comprehensive Center on Obesity in Chicago, in an accompanying editorial.

“Both reports emphasize the benign nature of fat accumulation outside the abdomen,” Landsberge said. “In both studies, the detrimental effect of visceral fat accumulation and its surrogate, waist circumference, were clearly demonstrated, confirming older studies showing that waist circumference is a risk factor even in normal-weight individuals.”

The message for practicing clinicians is that calculating body mass index and measuring waist circumference are valuable tools in assessing cardiovascular risk in overweight and obese patients, Landsberg concluded.